1. Field of the Invention
The present invention relates to a process for forming an oxide film which is capable of suitably forming an oxide film, as one of fundamental techniques constituting the electronic device fabrication process, an apparatus for forming an oxide film which can preferably be used in such an oxide film-forming process, and an electronic device material which can preferably be formed by using the oxide film-forming process and apparatus. The process for forming an oxide film according to the present invention can preferably be used for forming materials for semiconductors or semiconductor devices (such as those having an MOS type semiconductor structure, and those having a thin film transistor (TFT) structure) or liquid crystal devices.
2. Related Background Art
Along with an increase in the degree or scale of integration of semiconductor devices in recent years, the element isolation technique tends to be shifted from LOCOS (Local Oxidation of Silicon; isolation by a field oxide film) to STI (shallow trench isolation; isolation by a trench groove). This is because the STI technique may easily provide an advantage that deeper and more reliable isolation can be attained.
When the STI is used, a highly reliable oxide film is first formed as a base oxide film on the surface of a trench groove, and then the trench groove is filled with an oxide film by using chemical vapor deposition (CVD), etc. Heretofore, in this case, the base oxide film has been formed by using a thermal oxidation process.
In the above thermal oxidation process, a high temperature of about 1000° C. is required. Accordingly, the above STI (trench oxidation) is only applicable to a very early step among the entire device fabrication process wherein the thermal damage due to the thermal oxidation is negligible.
When the above STI is adopted, the structure obtained therefrom naturally becomes a three-dimensional structure. In such a three-dimensional structure, it is necessary to oxidize surfaces of an Si substrate (or base material) having different crystal orientations. However, in the thermal oxidation process, the growth rate is dependent on the crystal orientation, and therefore the thickness of the resultant oxide film has a strong tendency such that it varies with different crystal orientations of the Si substrate in the trench groove having a film which has been obtained by the thermal oxidation process. Accordingly, when a minimum film thickness is intended to be secured, there are produced crystal orientation surfaces which have been oxidized undesirably thickly, and such a phenomenon has hindered the fabrication of finer devices.
Further, in order to enhance the reliability of oxide films, also in the thermal oxidation process, a wet oxidation process utilizing (H2O) or (H2O2) is used, and the development of an oxidation temperature technique capable of decreasing the rate is in progress. However, the thermal oxidation process still requires a temperatures of about 800° C. or higher. In order to secure the element isolation, the substrate is usually doped so as to provide a predetermined profile of an impurity. In this case, however, this technique tends to cause a problem such that the impurity is again dispersed in the processing due to the thermal oxidation process at 800° C. or higher.